This invention relates generally to laser apparatuses and more particularly to laser sources having a pump laser and source laser.
Laser apparatuses utilizing a source laser for emitting laser energy and a pump laser for exciting or pumping the source laser to produce the source energy are well known in the art. These type laser apparatuses are extremely useful where the source laser energy is in the submillimeter wavelength range. Such lasers can find use in scientific plasma diagnostics where the source laser energy is transmitted into the plasma to determine the absorption rate of the plasma. This type of diagnostics is particularly useful in determining the nuclear fusion properties of radioactive materials.
Another area of use of such devices is in atmospheric research to determine the amount of pollutants present in the atmosphere and whether any detrimental effects are occuring to the earth's ionosphere due to aerosol spray cans. A further use is sensing objects through dense fog or smoke in which the source laser energy is used similarly to radar to locate objects that are obscured by fog or smoke. Such lasers also may be useful in military applications.
The prior art source and pump laser systems utilize two separate and distinct resonating cavities; one cavity for the pump laser and another cavity for the source laser. In these prior art devices, the pump laser cavity includes an optical reflector and a partial optical reflector and transmitter axially spaced from the optical reflector. Laserable material is disposed between the two reflectors to produce pump laser energy at one frequency. Usually, the laserable material is excited by any type of excitation arrangement, such as a discharge or a flash tube. The source laser cavity includes a reflector axially spaced from the pump laser cavities partially reflective and transmissive reflector and a partially reflective and transmissive reflector axially spaced from the reflector. Laserable material is disposed between the reflector and the partially reflective and transmissive reflector which is excited by the pump laser energy to produce source laser energy at a different frequency. The reflector for the source laser cavity is made to be totally reflective of the source laser energy but will pass the pump laser energy into the source laser cavity.
In operation, the excitation arrangement excites the pump laserable material which produces pump laser energy. This pump laser energy oscillates between the two reflectors in the pump laser cavity. As the pump laser energy oscillates it passes through the laserable material thereby amplifying the pump laser energy. Once proper amplification has been reached a portion of the pump laser energy passes through the partially reflective and transmissive reflector of the pump cavity, through the reflector of the source cavity and then into the source cavity where it excites the source laserable material. Upon excitation the source laserable material produces the source laser energy which oscillates between the two reflectors of the source laser cavity. Each time the source laser energy oscillates through the source laserable material the source laser energy is amplified. Upon proper amplification a portion of the source laser energy is transmitted through the partially reflective and transmissive reflector for its intended use.
In a slightly modified prior art arrangement, the partially reflective and transmissive reflector of the pump laser cavity and the reflector of the source laser cavity are replaced with a single reflector which is partially reflective and transmissive of the pump laser energy and totally reflective of the source laser energy. However, the pump laser cavity and source laser cavity are still separate and distinct and the operation of the laser is essentially the same as previously described.
When making and operating a laser system that utilizes a pump laser to excite a source laser two criteria are used; First, the maximum possible energy from the pump laser should be coupled into the source laser cavity so that the highest amount of pump laser energy excites the source laserable material; Second, the losses of the pump laser energy inside the source laser cavity should be held to a minimum to achieve efficient use of the pump laser energy.
The above prior art devices do not entirely meet this criteria because with the two separate and distinct resonating cavities pump energy losses occur when it passes through the various reflectors and losses occur inside the source laserable cavity. Consequently, less than 50% of the pump laser energy is available for excitation of the source laserable material thereby resulting in inefficient operation.
An additional disadvantage of the two separate and distinct resonating cavities is that the intensity of the pump laser energy inside the source laser cavity is restricted by the numerous energy losses that occur when the pump laser energy passes into the source laser cavity and travels therein. Thus, the efficiency of the excitation of the source laser material is reduced.
Another disadvantage is that after the pump laser energy is coupled out of the pump cavity and into the source cavity a portion of the pump energy is reflected back into the pump cavity. Typically, less than one percent of the reflected pump laser energy is required to frequency pull the pump laser thereby creating amplitude instabilities of both the pump laser energy and the source laser energy. This also contributes to inefficient laser operation. This problem can only the eliminated by creating more pump laser energy loss between the resonating cavities by introducing energy absorbing material between the two cavities.
A further disadvantage of the two separate and distinct resonator system is the difficulty of critically aligning the two resonating cavities for proper operation. This is usually accomplished with additional optical elements placed between the two cavities thereby resulting in additional pump energy losses.
Another disadvantage is that the use of two separate and distinct resonating cavities with associated optical alignment devices results in relatively large and sensitive devices.